1. Field of the Invention
The present invention relates to a signal input/output device for receiving an electric signal transmitted from a sensor, a switch, or the like, and for sending an electric signal to a solenoid-operated valve manifold or the like.
2. Description of the Related Art
Signal input/output devices receive control signals generated by a controller, for example, and also transmit control signals for opening or closing a valve or for energizing an external load such as a lamp, a relay, or the like, based on the received control signals. Signal input/output devices also receive signals transmitted from a sensor, a switch, or the like that is mounted on a cylinder, and transfer the signals to a controller.
A signal input/output device of the above type is disclosed in Japanese Laid-Open Patent Publication No. 2002-23808. The disclosed signal input/output device includes a plurality of juxtaposed signal input/output units, wherein adjacent signal input/output units are connected to each other by a pin mounted on an end face of one of the signal input/output units, which engages in a hole defined in the other signal input/output unit (see paragraph “0015” of this publication).
However, the strength with which such adjacent signal input/output units are joined to each other by engagement of the pin within the hole is not very large. To increase the joining strength, the hole may be filled with an adhesive, so that the pin inserted in the hole can be held firmly in place by the adhesive. However, once the pin is fixed in position by the adhesive, it is difficult to separate adjacent signal input/output units, for the purpose of increasing or reducing the number of signal input/output units that are used.